Application specific integrated circuits (ASICs) and other types of ICs often include general-purpose I/O pins or pads used for interfacing with external circuitry. General-purpose outputs in particular allow firmware, software or other logic to control the logic state of an IC pin, and thus provide flexibility to use the IC in a variety of different system applications. In many host systems, however, external circuitry is powered from different supply voltages, and a general-purpose output buffer needs to operate from the supply level corresponding to the voltage supplied to the associated external circuit to ensure the data sent to the output is properly received. For example, one external circuit may operate at 5 V, while a second operates at 3.3 V, and a third external circuit operates at 1.8 V. To ensure that signals provided from a general-purpose output can be properly received by an external circuit, the corresponding supply voltage must be provided to the general-purpose output circuit. However, this requires the addition of an extra voltage supply pin for each configurable or programmable output buffer. External level shifting circuitry can be used to interface the general-purpose output with external circuitry, but that increases the cost and complexity of a given system design.